When using the current stable version of dev-python/msgpack (0.6.1) with the stable version of app-backup/borgbackup (1.1.8) the "borg mount" functionally is broken. It throws an exception with the message "TypeError: unpack() takes no arguments (1 given)" For details and supported versions see the following links. https://github.com/borgbackup/borg/issues/4245 https://bugs.gentoo.org/683012#c4 https://github.com/borgbackup/borg/blob/1.1.8/setup.py#L39
The current stable borgbackup depends on the working msgpack.